This invention relates to control for various plants such as thermal power plants, which employ a control system having an adjust control loop or on-off control loop or both control loops, and particularly to a control system for a plant considering the margin of the operation control value of individual apparatus constituting the plant.
The control system employed in, for example, a thermal power plant, makes use of a current control theory or the like as disclosed in JP-A-57-16719 (laid-open on Jan. 28, 1982), in addition to the PID control for the normal process control. In this control theory, the dynamic characteristics of the plant are converted into a model, thereby predicting variations or a value to arrive at from an amount of an input. In other words, feedforward control is employed for improving the precision of control. Feedforward control, as concretely described in the aforementioned publicly known example, employs a dynamic characteristic model of a superheater of a heat exchanger at each part of a boiler so as to predict a temperature of the vapor and to determine the amount of fuel which should be fed into the boiler.
In another system employed in a thermal power plant, as described in JP-A-62-207200 (laid-open on Sep. 11, 1987), a rate of a load change of a plant and a width of an allowable load change are limited by a magnitude of a rate of load change as expressed in a number of times of load change per unit time with respect to the turbine and generator as individual parts. This system considers conditions of the turbine and generator of individual parts as limits to the loads on the plant.